2x+2y+2z=390 (1)
4x+3y+2z=615 (2)
5x+4y+2z=760 (3)
(2)-(1)
2x+y=225 (4)
(3)-(2)
x+y=145 (5)
(4)-(5)
所以
x=80
y=145-x=65
z=(390-2x-2y)/2=50